Extended Forecast Discussion NWS Weather Prediction Center College Park MD 323 PM EST Tue Jan 10 2023 Valid 12Z Fri Jan 13 2023 - 12Z Tue Jan 17 2023 ...Unsettled and Active Pattern Continues for Western U.S. with focus on California Atmospheric Rivers... ...Overview and Guidance/Predictability Assessment... The parade of upper level troughs entering the West coast will continue into the medium range period. The latest guidance has trended faster than previous cycles with the broad scale flow of systems across the CONUS. A deterministic general model blend consisting of the 00z suite of EC/CMC/UK models and the 06z GFS was used to capture the departure of an East Coast system and the arrival of a pair of upper troughs in the West on days 4 and 5 not to mention the amplification of a central CONUS ridge. The 06z GFS and 00z CMC were more progressive and preferred to the 00z EC regarding the departing East Coast system. This is reflected by lower totals in our official QPF. 06z GEFS and the 00z ECE were introduced to the blend on day 5 to moderate some of the deep amplification taking place in the deterministic guidance. The 00z CMCE was introduced by day 6 and the GFS phased out by day 7 when the blend consisted of predominantly ensemble means. ...Weather/Hazard Highlights... Unsettled and active weather is expected to continue across portions of the West as a series of atmospheric rivers move onshore. The highly amplified pattern mentioned above will help focus the best moisture transport and rainfall along the immediate northwest California coast into Friday, and further up the Pacific Northwest coast affecting coastal regions of Oregon and Washington. However, by this weekend, another strong weather system approaches central California and will bring another round of widespread precipitation. This system will impact a larger area of California with even more heavy rainfall threats. Worsening flooding or delayed improvement of ongoing issues is possible again across a very over-saturated coastal central to southern California while the higher elevations of the Sierra see heavy snowfall. As the energy moves inland on Sunday, rain and higher elevation snows are possible in the Southwest, and eventually return flow out of the Gulf of Mexico may increase precipitation chances into the Plains/lower Mississippi Valley as well. Meanwhile, back to the East, most of the precipitation will likely have exited the East Coast by early Friday, except for some lingering, and locally heavy, rainfall along the New England Coast. Any snowfall with this system likely remains confined to higher elevations and locations well inland. As a secondary low pressure area develops off the Northeast coast, there is some potential for wrap back snows across parts of the Northeast into Saturday, but this evolution and threat is highly uncertain and dependent on exact proximity of the low to the coast. Parts of the Northeast could be well above normal to start on Friday, but should trend back to normal this weekend. Generally warmer than normal temperatures are expected across the Central U.S. through the period, particularly by later this weekend into early next week where parts of the Plains and into the Midwest could see high temperatures 15 to 20 degrees F above normal. Even more impressive will be the very warm nighttime lows, with readings 20 to 25 degrees F above normal across the Mississippi Valley and into the Midwest Monday-Tuesday. Kebede/Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of the Northeast, Fri, Jan 13. - Heavy rain across portions of the Pacific Northwest, Fri, Jan 13. - Heavy rain across portions of California and the Pacific Northwest, Fri-Mon, Jan 13-Jan 16. - Heavy rain across portions of California, Sat, Jan 14. - Heavy snow across portions of California, Sat-Mon, Jan 14-Jan 16. - Flooding likely across portions of California. - High winds across portions of the Southern Rockies, the Southern Plains, and the Southwest, Sun, Jan 15. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml